The present invention relates to motor control and, more particularly, to a system and method for controlling operation of an actuator motor during a retract condition in a hard disk drive.
A hard disk drive generally includes a stack of rotating disks or platters and a spindle motor that is controlled to cause the disks to rotate. Data is generally stored in the form of a sequence of magnetically polarized regions on the surface of the disk. The sequences, known as tracks, typically appear as concentric circles on the disk.
A read/write head, which is sensitive to changes in magnetic flux, reads and/or writes data to the disks as it is supported by an arm above the surface of the disks in close proximity relative to the disks. An actuator motor (known as a xe2x80x9cvoice coil motorxe2x80x9d or VCM) controls the positioning of the arm for moving read/write heads relative to the surface of the disks. As a disk rotates under the read/write head, the read/write head xe2x80x9cfliesxe2x80x9d on a thin cushion of air created by the motion of the disk. The read/write head reads data from a disk by sensing flux changes on the magnetic surface of an associated disk as it passes beneath the read/write head.
Under certain circumstances, it is desirable to move a read/write head to an area of the disk on which data is not stored or to a location off the disk, referred to as a landing zone or ramp. This may occur when power to the hard drive is lost, when the supply voltage sags, or when the drive is xe2x80x9cparkedxe2x80x9d by the user for any reason. When a retract is requested for a non-critical reason, such as a request by the user to park the hard disk drive, a slow retraction of the read/write head is desirable so as to avoid potential damage to the read/write head caused by sudden acceleration of the head relative to the disk. However, when the hard disk drive supply voltage decreases below a critical level, such as at power failure, fast retraction of the read/write heads is desirable. The read/write head may xe2x80x9ccrashxe2x80x9d into the disk if the disk rotation rate decreases below a critical level. Therefore, when power to the spindle motor is lost or diminished, the head must be moved quickly to a safe landing zone of the disk where it can xe2x80x9cland.xe2x80x9d
If a read/write head is moving when a retract is requested, a brake control function may initially be applied to the VCM for a predetermined time to help slow down the VCM. The brake control function typically is implemented by shorting the VCM. Next, a fixed voltage is applied across the VCM to move the read/write head to its landing zone at a predetermined velocity. However, in certain circumstances, the braking function and fixed voltage may be insufficient to move the read/write head to the landing zone prior to crashing into the disk. The deficiency becomes even more pronounced when a fast retraction is required, such as when retract is initiated during a seek command. During a seek command, the VCM is driven at or near its maximum velocity so as to rapidly move the head to a desired track on the hard drive.
If a read/write head is unable to reach its landing zone, a read/write head and/or its support structure may impact the hub or spindle of the hard disk drive, dislodging small fragments of material, such as aluminum, from the hub or spindle. The fragments may rest on the surface of the disk, creating an uneven surface that would disturb the flight of the read/write head over the disk or damage data on the disk. Moreover, an impact between the read/write head and the disk may damage the disk and/or the read/write head.
The present invention provides a system and method for controlling an actuator for retracting a read/write head of a hard disk drive system, such as may occur in response to detecting a fault condition of the disk drive system. The present invention, for example, may be implemented in connection with a multi-stage retract sequence.
By way of example, one stage of the retract sequence may employ deceleration followed by braking of an actuator motor. The deceleration may be implemented, for example, by energizing an associated actuator in a selected direction (e.g., by current control) for a predetermined time period. After the deceleration, the actuator motor may be braked, such as by shorting input terminals of the actuator motor to a predetermined voltage level. By rapidly decelerating the read/write head in this manner, the overall retract time may be improved. As a result, damage to the disk and/or the read/write head may be mitigated. In accordance with another aspect of the present invention, the deceleration feature may be enabled or disabled in response to a user-selectable input.
A subsequent stage of a retract sequence, in accordance with an aspect of the present invention, may utilize a sensed back EMF of the actuator motor to adjust energization of the actuator motor. The sensed back EMF is functionally related to the speed of the motor during retract. A sensor may be employed to sense the back EMF, such as during a sampling interval during which the motor is not energized. The sensed back EMF may then be compared with a target back EMF to determine if the actuator is moving too slow or too fast. The velocity of the actuator motor may then be adjusted based on the results of the comparison to move the read/write head toward its rest position at a desired velocity. According to yet another aspect of the present invention, the back EMF control feature may be enabled or disabled in response to a user-selectable input. As a result of controlling retract in accordance with an aspect of the present invention, damage to the disk and/or the read/write head may be mitigated and the read/write head may be moved to a desired landing zone in an efficient and rapid manner.
Yet another aspect of the present invention provides a disk drive read/write head retract system. The system includes a controller having at least two operating modes in response to receiving a retract request signal. When the controller is in a first operating mode, it is operable to provide a deceleration control signal for decelerating an actuator in a selected direction for a first time period. The controller operates in a second operating mode after the first operating mode to provide a brake control signal for braking the actuator for a second time period.
Another aspect of the present invention provides a disk drive read/write head retract system. The system includes a controller for controlling energization of an actuator. A back electromotive force (xe2x80x9cEMFxe2x80x9d) sensor senses back EMF of the actuator. In response to a retract request signal, the controller is operable to control the actuator based on the sensed back EMF relative to a target back EMF value, which target back EMF value may be selected by a user.
Still another aspect of the present invention provides method for controlling an actuator for retracting a read/write head in a disk drive system. The method includes decelerating the actuator in a first direction for a first time period in response to retract request signal and then braking the actuator for a second time period.
Another aspect of the present invention provides a method for controlling an actuator for retracting a read/write head in a disk drive system. The method includes sensing back electromotive force (xe2x80x9cEMFxe2x80x9d) of the actuator and controlling energization of the actuator based on the sensed back EMF relative to a selected target back EMF.
To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.